Wireless communication devices are becoming more and more common-place in today's society. During wireless communication, a wireless transmitter encodes a message as a digital bit stream (e.g., a stream of logical “1”s and “0”s), and then modulates the digital bit stream onto a carrier wave to generate a stream of symbols, where the symbols are somewhat akin to an alphabet for communicating devices. This stream of symbols is then transmitted to an intended wireless receiver over a wireless transmission medium (e.g., through the atmosphere). Upon accurately receiving the stream of symbols, the intended wireless receiver demodulates the symbols and decodes the digital bit stream to recover the originally transmitted message. Often, the receiver provides the message to an end user in the form of an audio and/or visual display (e.g., LCD screen and/or speaker), for example.
One type of modulation that wireless devices can use during such communication is polar modulation. FIG. 1A shows an example of a conventional polar modulator 100 that includes a digital signal processor 102, a voltage controlled oscillator (VCO) (or a digitally controlled oscillator (DCO)) 104, and an antenna 106. As discussed in more detail below, these components work in coordinated fashion to modulate a digital bit stream onto a carrier wave as a stream of symbols, thereby enabling wireless transmission via the antenna 106.
To illustrate one example of how symbols can be used to transmit a digital bit stream, FIG. 1B shows a voltage vs. time plot for two symbols consistent with a binary phase shift keying (BPSK) scheme. Relative to a carrier wave with a 0° phase offset (108), Symbol A 110 (which can be assigned to a logical “1”) is transmitted with a 0° phase offset (i.e., in phase with the carrier wave 108). Symbol B 112 (which can be assigned to a logical “0”) is transmitted with a 180° phase offset relative to the carrier wave 108. FIG. 1C shows a phase plot 114 of Symbol A 110 and Symbol B 112. Consistent with FIG. 1B, Symbol A 110 is characterized by a phase offset of 0° and Symbol B 112 is characterized by a phase offset of 180°, wherein both symbols have the same amplitude as evidenced by their equal radii as measured from the origin 114, which may also be referred to as a “zero crossing point.”
FIG. 1D shows an example of how Symbol A 108 and Symbol B 110 can be used to transmit a digital bit stream 116 (e.g., a digital bit stream of “101100”). As shown, symbols are transmitted during respective symbol periods. For example, a first symbol (e.g., Symbol A corresponding to a logical “1” value), is transmitted during a first symbol period TS1; a second symbol (e.g., Symbol B corresponding to a logical “0”) is transmitted during a second symbol period TS2; and so on. To transmit these symbols, the digital signal processor 102 abruptly alters a time-varying phase modulation control signal 118 to induce a phase shift in the output of the VCO-DCO 104. As can be seen from the bottom waveform of FIG. 1D, when the DSP abruptly changes the phase modulation control signal 118, a “frequency spike” occurs in the VCO-DCO output. For example, at symbol boundary TS1 the DSP 102 alters the phase output from the VCO-DCO 104 to attempt to induce an immediate 180° phase shift between symbol A (used just prior to symbol boundary TS1) and symbol B (used just after symbol boundary TS). However, because this sudden 180° phase shift requires a near infinite frequency (120) to achieve the phase change, this 180° phase shift is difficult to achieve with a VCO and/or DCO.
Hence, the present disclose has developed improved techniques for performing polar modulation. Among other advantages, at least some of these techniques make 180° phase shifts between adjacent symbols easier to achieve compared to conventional techniques.